Convert bin/files to ObjectQuery

Summary: Ref T603. This has some custom logic which ObjectQuery can now perform more simply and more correctly.

Test Plan: Ran bin/files purge F1, bin/files purge D1, bin/files purge --all.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T603

Differential Revision: https://secure.phabricator.com/D7180